The present invention relates to the field of high-quality audio loudspeakers and more particularly to loudspeakers which overcome the drawbacks of backwave interference and cancellation as well as other problems with high-fidelity speakers. The speakers of the present invention utilize multiple drivers in a multipolar configuration which are sealed in an isobaric chamber.
Loudspeakers are essentially transducers which convert electrical energy into physical, acoustical energy. The design of typical basic loudspeakers has not changed for decades. Generally, a loudspeaker driver consists of a frame or housing, a cone or other diaphragm attached to a voice coil, a surround and spider suspension and a permanent magnet. Sound is created by moving the diaphragm to create sound waves in the air around the diaphragm. This is accomplished through electromagnetic attraction and repulsion of the voice coil. The outer periphery of the diaphragm is connected to the housing or frame by a flexible surround which allows the diaphragm to move freely and helps somewhat to keep the diaphragm and voice coil in proper alignment. The voice coil is typically a coil of wire which forms an inductor. As electrical current passes through the coil it produces a magnetic field. The voice coil is placed in close proximity to a permanent magnet which provides a permanent magnetic field which react with the variable magnetic field of the coil thereby causing the coil to be repelled or attracted according to the field of the coil and the polarity and magnitude of the coil current. The spider and surround keep the coil in precise alignment with the permanent magnet so that minute changes in current in the coil can accurately produce diaphragm movement and sound.
The physical characteristics of drivers can make them more suitable for reproducing sounds in certain frequency ranges. High frequency sound requires a driver that can react quickly, but which does not need a diaphragm that must displace a substantial distance. Low frequency sound requires a driver that can displace longer distances, but which does not need to react as quickly. Consequently, larger drivers, called woofers, are typically used to reproduce low frequency sound while very small, rigid drivers, called tweeters, are used for high frequency sound. A high-quality loudspeaker will generally have multiple drivers for reproducing sound in a variety of frequency ranges. Many loudspeakers will have at least a woofer, midrange and a tweeter to reproduce the entire audible sound spectrum, however, as the following disclosure will reveal, this can be achieved in other ways.
One problem inherent in typical driver design is the xe2x80x9cbackwavexe2x80x9d created when the diaphragm rebounds from an extended position. This creates a sound wave which emanates from the back of the diaphragm which, if not controlled, may interfere with and even cancel the primary sound wave created by the diaphragm.
One method of dealing with backwave interference is to mount the driver in a sealed enclosure that will absorb the majority of the backwave preventing it from reaching the listener. This is commonly known as an xe2x80x9cacoustic suspensionxe2x80x9d speaker. Another popular method of dealing with backwave emissions is to allow part of the wave to reach the listening area through a vent or port. This is known as a xe2x80x9cbass reflexxe2x80x9d design. Yet another method involves the use of a passive radiator or xe2x80x9cdrone driverxe2x80x9d which vibrates with the backwave thereby absorbing energy and helping eliminate the backwave. All of these methods help somewhat to eliminate backwave interference, however they do so at the cost of lost energy and performance.
Backwave interference can also be dealt with using a bipolar speaker configuration. The typical bipolar configuration utilizes two identical drivers which are mounted in the front and back of a speaker enclosure. These two drivers are driven in-phase so that identical waves are emitted from the front and back of the enclosure. This eliminates the backwave cancellation problem because the waves are in-phase, but the drivers can suffer from a decreased response and lost energy due to the need to overcome increased pressure in the enclosure.
An additional problem with current speaker technology is caused by misalignment of the voice coil with the permanent magnet due to distortion of the diaphragm or cone. Driver surrounds and spiders must be flexible to provide the necessary response to electrical input, but this makes the driver diaphragm extremely susceptible to unequal air pressure across its surface area. As a diaphragm encounters unequal air pressure due to enclosure discontinuities or air flow patterns, the diaphragm distorts causing the attached voice coil to rotate off its central axis. This causes the precisely balanced magnetic fields of the permanent magnet and the voice coil to misalign thereby causing an inductive variance and increased current draw from the amplifier. This results in decreased power handling, poorer response and inaccurate reproduction of sound.
Pressure problems encountered with in-phase bipolar designs can be overcome by using an out-of-phase configuration. In a typical out-of-phase bipolar configuration, identical drivers are mounted facing in opposite directions connected by an isobaric chamber. However, one driver is wired in reverse polarity to the other so that both driver""s diaphragms move in the same direction despite facing in opposite directions. This configuration allows the isobaric chamber to remain at a constant volume and pressure. As one diaphragm moves outward, the other moves inward by an equal amount. While the pressure problems are reduced, interference between the drivers remains a problem.
The present invention is a multiple driver, resonantly-coupled loudspeaker which reduces or eliminates the problems of the prior art and provides greatly increased power handling, extended, more linear, response to low frequencies, increased midrange response and lower inter-modulation distortion.
The present invention comprises a plurality of drivers which are arranged and oriented such that the back wave from at least one driver may coincide with the front wave of at least one other driver thereby causing interference between the back wave and the front wave. The synchronization circuit of the present invention effectuates a phase shift in the signal transmitted to some of the driver so that the interference between back wave and front wave results in reinforcement of the overall driver output. The drivers of the present invention may be arranged in a multipolar, isobaric configuration, as in a preferred embodiment, or they may be arranged in another configuration which may benefit from the synchronization and reinforced output of the present invention.
In some embodiments of the present invention, an even number of drivers are mounted in an isobaric enclosure which is sized and oriented to enclose the drivers within a minimal volume. The drivers may be oriented to face into the enclosure or face outward from the enclosure. Drivers used in the present invention are divided into pairs with one driver in each pair being directed toward the exterior of the loudspeaker assembly and one driver being directed into an interior acoustical chamber. A novel secondary crossover network is utilized in the present invention to integrate the drivers in this multipolar, isobaric configuration.
Crossover networks, both passive and active, are known for filtering the input signals to loudspeaker drivers. Low pass, high pass, band pass and band reject filters are used to limit the signal frequencies sent to a given driver. These conventional crossover networks may be used with the present invention, however a novel secondary network is also used between the paired drivers themselves to synchronize the paired driver""s movement. Conventional out-of-phase multipolar speakers are wired with direct reverse polarity and no secondary crossover. The secondary paired-driver crossover network of the present invention is believed to adjust the phase relationship between the paired drivers so that the backwave from the external driver coincides with and reinforces the frontwave from the internal driver thereby increasing the amplitude of the combined wave emitted from the internal driver""s acoustical chamber. This reinforcement can be measured by measuring the response to square wave signals at the port in the internal driver""s acoustical chamber.
Accordingly, it is an object of some embodiments of the present invention to provide a loudspeaker with an increased frequency range.
Another object of some embodiments of the present invention is to provide a loudspeaker with greatly reduced inter-modulation distortion.
A further object of some embodiments of the present invention is to provide a loudspeaker with better power handling
An additional object of some embodiments of the present invention is to provide a loudspeaker with quicker response.
A still further object of some embodiments of the present invention is to provide a loudspeaker with a lower resonant frequency.
Another object of some embodiments of the present invention is to provide a loudspeaker which provides a full range of response throughout midrange frequencies without the use of a conventional midrange driver.
Yet another object of some embodiments of the present invention is to provide a loudspeaker with a greater, more linear dynamic range.